so I get about 1 full cup of water evaporated everyday in my 20 gallon tank, which is kind of a lot and increases the Salinity from 1.0245 to 1.025 each day. so I top off the water everyday to get the stability in salinity!
now my pH used to be a stable 8.0 with KH of 9.0. this week I noticed the pH dropping to 7.8 !! with same KH.

question is : do I need to bring the de-chlorinated tap water's pH to 8.0 for top offs ? my tap water has pH of about 7.3.

furthermore, since I'm using tap water (nitrates are zero) do I still need to add chemical supplements such as Iodine? or does the tap water top off take care of that._________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral

Part of your stability problem is due to the small volume of your tank water; if you could go with a 30 or 40 gallon minimum, or perhaps add a large sump, you may find this easier to maintain. What type of coral are you keeping; soft coral, SPS...? What is the goal for your system; are you planning on more corals, and what types? I see three anemones on your list; I hope you are aware that most anemones are unsuitable for captivity in the average marine aquarium; just food for thought.

Regarding the pH of your top off water; I would be far more concerned about the possibility of heavy metals like copper in your tap water; and make sure you're not adding even MORE problems with these water changes, because many cities have surprisingly high levels of nitrates and phosphates in the tap water. That's right, test your tap water! Reverse Osmosis (RO) water may be required and is a common choice among reefers, but to be really effective against some problems (high phosphates for example) you may need two de-ionization stages (in series) on the RO filter. Yes, these cartridges will need replacing. You're asking great questions; and I wish you the best of success. Here's a couple of links with more info on supplements, buffers and iodine:
http://fins.actwin.com/reefkeepers/reefkeeper1.htmlhttp://www.advancedaquarist.com/issues/mar2003/chem.htm_________________Keepin' marines happy for 25 years

How mature is the tank?
If it is still young the water should still have buffering abilities and should stabilize the pH on its own accord with the help of a sand bed or crushed coral substrate.
I have evaporating plates over my tank. They help reduce the amount evaporated in a week. Is the tank in the sun a lot during the day?

How mature is the tank?
If it is still young the water should still have buffering abilities and should stabilize the pH on its own accord with the help of a sand bed or crushed coral substrate.
I have evaporating plates over my tank. They help reduce the amount evaporated in a week. Is the tank in the sun a lot during the day?

well the tank itself is about 2 months old, but I basically took it from a 3 year old tank !, took the water, and live rock form a 500 G tank, and put it in mine, and started it right up
the temperature is at constant 82 F.
I have taken the glass top off, (cause I thought it would filter out the light spectrum and have 2 T5 lights on the tank (2x24 watts)
what is evaporating plate ? just like a glass top ?_________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral

Part of your stability problem is due to the small volume of your tank water; if you could go with a 30 or 40 gallon minimum, or perhaps add a large sump, you may find this easier to maintain. What type of coral are you keeping; soft coral, SPS...? What is the goal for your system; are you planning on more corals, and what types? I see three anemones on your list; I hope you are aware that most anemones are unsuitable for captivity in the average marine aquarium; just food for thought.

Regarding the pH of your top off water; I would be far more concerned about the possibility of heavy metals like copper in your tap water; and make sure you're not adding even MORE problems with these water changes, because many cities have surprisingly high levels of nitrates and phosphates in the tap water. That's right, test your tap water! Reverse Osmosis (RO) water may be required and is a common choice among reefers, but to be really effective against some problems (high phosphates for example) you may need two de-ionization stages (in series) on the RO filter. Yes, these cartridges will need replacing. You're asking great questions; and I wish you the best of success. Here's a couple of links with more info on supplements, buffers and iodine:
http://fins.actwin.com/reefkeepers/reefkeeper1.htmlhttp://www.advancedaquarist.com/issues/mar2003/chem.htm

well the Tap water almost has no nitrates in it, but phosphate a bit, which is removed by my skimmer prety fast as it seems. I'm from toronto, canada, I have been reading tap water chemistry from other places, and I'm amazed with the water we have here in Toronto!!_________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral

Just a few notes on phosphates, there is some confusion among aquarists on this...

Phosphorus in seawater comes in two basic forms; there are inorganic phosphates (also called orthophosphate), and another form called organophosphate. It should be understood that skimmers will not directly remove inorganic phosphates (PO4-3) from your water.

Skimmers remove organic compouds that contain phosphorus, so indirectly they do have a positive effect. Skimmers can remove certain organic molecules (connected to proteins) BEFORE they can be broken down into orthophosphates, but once the inorganic phosphates are there you will need another plan for removing them.

Couple of links below for more info on this, but basically; if your top off water contains a lot of inorganic phosphates (orthophosphate), your skimmer is not really going to solve that problem. For example, in 2005 New York City officials reported that water samples showed phosphate levels as high as 3 ppm! I'm glad you are researching tap water chemistry; many reef hobbyists have no idea how many problems can be traced to their source water... you're on the right track.

Just a few notes on phosphates, there is some confusion among aquarists on this...

Phosphorus in seawater comes in two basic forms; there are inorganic phosphates (also called orthophosphate), and another form called organophosphate. It should be understood that skimmers will not directly remove inorganic phosphates (PO4-3) from your water.

Skimmers remove organic compouds that contain phosphorus, so indirectly they do have a positive effect. Skimmers can remove certain organic molecules (connected to proteins) BEFORE they can be broken down into orthophosphates, but once the inorganic phosphates are there you will need another plan for removing them.

Couple of links below for more info on this, but basically; if your top off water contains a lot of inorganic phosphates (orthophosphate), your skimmer is not really going to solve that problem. For example, in 2005 New York City officials reported that water samples showed phosphate levels as high as 3 ppm! I'm glad you are researching tap water chemistry; many reef hobbyists have no idea how many problems can be traced to their source water... you're on the right track.

hmmm thanks, those are new info to me ! have a lot to read for tonight.
I have placed some small lights on top of the floss in my HOB filter, and I can see a lot of algae growing on the floss (from white to GREEN in less than 24 hours) so I thought by doing this, I am growing algae which eats up the nitrate and phosphate in the water, and cleaning the floss daily, would lower them both, it has been working, but gotta read more to see what type of phoshate it is that I'm removing !_________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral

Yep, algae can actually be an effective part of controlling phosphates, including both microalgae and macros like Caulerpa and Chaetomorpha.

Many aquarists also employ granular ferric oxide (GFO) and others use bacterial blooms triggered by addition of carbon sources like sugar or vodka. Be advised, each of these methods has its pros and cons; the article I linked will give you a good overview of all of them; your research will lead to success..._________________Keepin' marines happy for 25 years